The present invention relates generally to digital radio communications system, and specifically to a packet radio communications system having mobile packet terminals which may move randomly across boundaries between service zones of adjacent base stations.
Generally, packet radio communications system has a central station that administers a plurality of base stations each covering a respective service zone. During a transmit mode, a mobile station in a given service zone transmits an up-direction packet in response to a polling packet from the base station of the given zone. When the up-direction packets of a predetermined number have been received by the base station, it assembles them into a data block and sends it to the central station. During a receive mode of the mobile station, down-direction data packets are transmitted from the central station as a single data block to the base station where it is disassembled into individual packets and transmitted in sequence to the mobile station. When the mobile station moves across a zone boundary, leaving the service zone of a first base station and entering the zone of a second, adjacent base station during a communication with the first base station, the latter attempts to continue the communication until a timeout period is lapsed. If the mobile station attempts to establish a connection with the second base station within the timeout period, the second base station rejects it as an unauthorized attempt. When the timeout period has lapsed, the mobile station realizes that it is unable to continue communicating with the first base station and attempts to establish a new communication with the second base station. Even if this attempt is successful, the mobile station must retransmit to it a copy of the whole contents of data which have been transmitted to the first base station since the lapse of the timeout period is regarded as an abandonment of a communication. As a result, the current digital radio communications system experiences a low throughput when a mobile station crosses a zone boundary in the midst of a session.